jsonschema is an implementation of JSON Schema for Python (supporting 2.6+ including Python 3).

>>> from jsonschema import validate

>>> # A sample schema, like what we'd get from json.load()
>>> schema = {
...     "type" : "object",
...     "properties" : {
...         "price" : {"type" : "number"},
...         "name" : {"type" : "string"},
...     },
... }

>>> # If no exception is raised by validate(), the instance is valid.
>>> validate({"name" : "Eggs", "price" : 34.99}, schema)

>>> validate(
...     {"name" : "Eggs", "price" : "Invalid"}, schema
... )                                   # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
    ...
ValidationError: 'Invalid' is not of type 'number'

• Full support for Draft 3 and Draft 4 of the schema.
• Lazy validation that can iteratively report all validation errors.
• Small and extensible
• Programmatic querying of which properties or items failed validation.

v1.4.0 adds a better interface for creating and extending validators in the form of jsonschema.validators.create and jsonschema.validators.extend. The documentation is still a bit lacking in this area but it's getting there. See the tests in jsonschema.tests.test_validators and the source code if you'd like to try it out now.

It also fixes a number of issues with ref resolution, one for array indices (#95) and one for improper handling of unknown URI schemes (#102).

jsonschema uses the wonderful Tox for its test suite. (It really is wonderful, if for some reason you haven't heard of it, you really should use it for your projects).

Assuming you have tox installed (perhaps via pip install tox or your package manager), just run tox in the directory of your source checkout to run jsonschema's test suite on all of the versions of Python jsonschema supports. Note that you'll need to have all of those versions installed in order to run the tests on each of them, otherwise tox will skip (and fail) the tests on that version.

Of course you're also free to just run the tests on a single version with your favorite test runner. The tests live in the jsonschema.tests package.

There's a mailing list for this implementation on Google Groups.

Please join, and feel free to send questions there.

I'm Julian Berman.

jsonschema is on GitHub.

Get in touch, via GitHub or otherwise, if you've got something to contribute, it'd be most welcome!

You can also generally find me on Freenode (nick: tos9) in various channels, including #python.